I got tired screwing phone into the holder (see here: https://www.printables.com/model/80163-bike-holder-for-phone-and-drink ), so I needed something faster and easier. In to the rescue comes @azure93 who's design you can find here: https://www.thingiverse.com/thing:2338865

If you print this with 60mm/s speed, it takes less than 2 hours to print and uses only 27 grams of filament. Use 3 walls to get enough rigidity. I used PLA and the flex is just perfect.

You may need to change the size to fit your phone, this file is for Xiaomi M10T which is 79mm wide. Just open included 3MF file on 3D Builder (free from windows store, or could already be included in your OS) and do split on the wing holding the phone, keep both sides and move the piece you just cut according your own phone measurements.