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

[j3gq_imp]

I don't know if this is what you need/want, and it won't work well while parked ... but ...
If you funnel "a mostly laminar stream of air" from around the position of the head light onto the backside of your phone, your i-phone will shut down less often - guarantied !
Why would this work ? even on a warm day the air around you is less warm than the surface temp of your phone (think solar radiation), and the natural air-stream from the frond of the bike is often impeded (turbulent) because of cables, phone holder, shields etc. Finally this air stream (even at 80F carries away more heat than the solar radiation dumps into the device.
How to do that ? your choice of funnel material, from cardboard to metal, color white or silver, and a creative way to fix it to the handle bar.

If you try it (it isn't hard to do or expensive) please report back !