iPhone sun shade ?

[E11even_Hunnit]

I do not text while riding.....only have two hands

..but now seriously, you can put it in a soft-black plastic box with reinforced bottom (like a wrap up) with 1-2" high side wall that prevents the sun from penetrating your screen... simple $3 device...
It may work for you if you have suitable phone holder....

I build this U shape shade for my GPS

This along with a matte screen protector will be as good as it's gonna get, unless you buy a larger headlight fairing and find a way to tuck it inside with the right RAM bracket where it's under the shade but still visible, and that in itself will be subject to change based on the sun angle while you're in motion

Some years back, I installed Parrot's android Headunit on my Lexus and I had the same issue with reflection and glare during the day, the matte screen protector helped