I just look through the Oregon Revised Statutes.
Nothing in there about cell phone mounts.
ORS 815.220 Obstruction of vehicle windows.
• penalty
(1) A person commits the offense of obstruction of vehicle windows if the person drives or moves on any highway or owns and causes or knowingly permits to be driven or moved on any highway any vehicle with windows obstructed in a manner prohibited under this section.
(2) The windows of a vehicle are obstructed in a manner prohibited by this section if any material that prevents or impairs the ability to see into or out of the vehicle is upon any vehicle window described in this subsection. This subsection applies to any sign, poster, one-way glass, adhesive film, glaze application or other material if the material prevents or impairs the ability to see into or out of the vehicle. This subsection only applies to the following windows of the vehicle:
(a) The front windshield.
(b) The side-wings.
(c) The side windows on either side forward of or adjacent to the operators seat.
(3) Nothing in this section prohibits safety glazing materials of a type that conforms to standards established under ORS 815.040 (Standards for window and windshield material).
(4) Nothing in this section prohibits placement of permits in accordance with the provisions of ORS 803.650 (Placement of permits in vehicles) or with rules adopted by the Department of Transportation under ORS 803.650 (Placement of permits in vehicles).
(5) Nothing in this section prohibits the application of tinting material to the windows of a motor vehicle in compliance with ORS 815.221 (Tinting).
(6) The offense described in this section, obstruction of vehicle windows, is a Class D traffic violation. [1983 c.338 §490; 1985 c.16 §255; 1987 c.166 §5; 1995 c.263 §4; 1995 c.383 §91; 2003 c.158 §5; 2013 c.199 §1]
Not a lawyer, drove all over Oregon, Washington, Idaho Montana, and Canada with a Garmin stuck to the windshield. No worries.