I found and printed ficacador's original version and it worked well for the phone I had but I saw comments saying it wouldn't work for someone's larger phone so I thought why not remake it in openscad then it can be customized for someone's specific phone

you will need to also download openscad and MoonCactus's gopro customizable mounts scad file linked below. Note you will need to have the gopro_mounts_mooncactus.scad file in the same folder as phoneHolder.scad file for it to work

https://openscad.org/
https://github.com/MoonCactus/gopro_customizable_mounts
https://www.thingiverse.com/thing:62800

Usage:
if you're phone is between 52mm and 70mm in width, longer than 110mm, and thinner than 10mm you can use the already made stl (from my guesstimation)

to customize this though there are 3 main variables at the top of the scad file that should do most of the modifying needed
armLength is the length of the arms default 90 because this is about what ficacador had.
armAngle is the angle from base ( opposite side of the base) default 128 because this is also about what ficacador had.
phoneThickness is max phone thickness (probably) default at 10mm also because that's about what ficacador had.

When your run this in openScad look in the console and you will see some extra ECHO lines noting the "resting width", "max width?", and "resting length"
These are using trig to calculate the approximate X/Y dimensions of the holder.

"resting width" is how far are the arm holders are from base if you measured straight perpendicular to the base out.
'max width?" is how far the arm holders would be perpendicular out if the arms were only 98 degrees from the base, so almost touching, Note I don't actually know how far these will be able to bend without breaking and I also doubt they will bend "straight" they will probably bend/curve instead so this only a guess.
"resting length" is how far apart the 2 arm holder parts when at rest. This will only get shorter when under tension so when when the phone is bigger than the resting width but on mine they are right at the corners of the phone so I wanted to note this here so if you increased the arms alot you knew if might be longer than your phone now so you would instead want to decrease the angle some to compensate.