Perhaps something like this will of use to you. It requires no license. It's not very cheap though.
BTW, GMRS radios do require a license.

LINK to GoTenna.

Your phone doesn't make noises in the right frequencies to be useful as a local radio.

If you only intend to ever use it in an emergency, then there are no limits.

Unlicensed people can operate in any band their equipment can handle in an emergency.

Now the odds are against someone doing so optimally if they have never operated the radio, and to operate the radio they may need a license.  That would be prudent.

But you could buy a baofeng and program in whatever channels you like and if you never used it except in an emergency you would be fine.

You can purchase a radio and transmit on FRS channels without a license. Like the previous post said, you can transmit on any frequencies in an emergency. I'm talking about a true emergency, not calling home to tell your wife you are running late.
You don't need to have a smartphone to operate a radio in a regular matter. I'm not sure what you are trying to accomplish with your smartphone. A smartphone can't be used to transmit on any frequencies except the ones used for cell phone communications. Besides that, a cellphone has very low transmit power. It's only designed to reach a closest tower withing line of sight. Perhaps you need to be more specific about what you are trying to accomplish.

The marine frequencies you are focused on are completely useless except when you are on the water. If you are on land, you would be better served to have a radio that can operate on the VHF aviation guard frequency, 121.5MHz. However, even that is going to be a crapshoot.

I'm not aware of a practical method to use your phone as a remote front end for a radio in a back country setting.

However, for your requirements, you would be much better served by something like an inReach (the Garmin versions are pricey, you can find the older Delorme versions for quite a bit less), or just a plain old PLB. Ocean Signal makes the smallest, but there are plenty of other choices. There are good deals on the older ACR units on eBay all the time, see my thread here.

Channel 16 you are referring to is one or the marine frequencies. As far as I know, you are not allowed to use marine radios for land to land communications. Many hunters use them anyway and I never heard anyone being penalized, unless they deliberately interfered with Coast Guard operations and have not stopped after being warned several times.
There may be some apps to link a marine radio to a smartphone. This is outside my area of expertise. Perhaps other members know more about this.
FRS radios are relatively small and portable to keep on a front strap of your backpack. In case of an emergency, you can simply read out your GPS coordinats to the party you are communicating with.

Now, if you get a ham license, there will be A LOT of options for you. It's a simple 35 question test that many 8 year old kids pass with flying colors. There are ham radio repeaters just about everywhere, including areas with poor on no cell service. You will also be able to use APRS feature in GPS equipped radios to communicate your position to others and you'll be able to see where other station is.
If you get a General or Extra class license you can use HF (shortwave) rigs to talk to stations around the globe. All you need is a small radio, a 12V power source and a simple wire antenna. Beware that this hobby can be very addictive.

http://androidradio.rfinder.net/

I can buy a buncha refurb'd ZTE phones and TYT HT's for that kinda money-but it may be what you're looking for?

You can snag an inReach off of eBay for under $300 and keep it fed with a service plan continuously for two and half years for that kind of money, and be much better off. Assured instant comm's anywhere, one button SOS, vice playing radio to save your life? Just sayin'...

Actually, there aren't. Go anywhere in the north country of NH and Maine and you are SOL, and that's just one example I happen to be personally familiar with. Relying on VHF/UHF comm's to save your life up there is a death sentence. Nobody to talk to, no APRS, either.

And, in an emergency, a working set of legs and arms to deploy it, and a sufficiently functioning brain to use it. Hurt, hypothermic, and/or in shock, getting that done might be a challenge! Compare the complexity of setting up and using an HF radio (or even a VHF radio) to make an emergency contact to simply pushing one button on a PLB, Spot or inReach device.

As you can tell, I'm not a big fan of ham radio for saving my life in an emergency, even though this is the ham forum

I feel ya, I'm happy as I can be with my $55 refurb ZTE and I don't enjoy DMR (like I should) not to mention I'm a cheap dude-$700 for almost anything that does not take diesel fuel or black-powder is beyond me!

I would not rely my life on any electronic gismo, period. The fact it that ham radios do work when everything else fails and there are repeaters in many areas of the country where cell phone coverage is non existent. There are plenty real world cases that prove this. I never said he will get coverage EVERYWHERE. He asked the question in the ham radio forum and I gave his the answers to my ability. Of course he is an adult and I'm sure he knows about satellite phones or satellite beacon services. Even then the sat phone or a beacon can fail or may not work in certain places. This is where rule # 1 comes handy: Never trust your life to an electronic gismo. He wanted a cheap smartphone that would link to a radio for emergencies.