So you're using the phone only ?
Sounds like it and yes, the small size is not only more difficult to see, but generally that also makes it much harder to see light wise (brightness) sometimes.
Trouble with any shade made, they will all make it hard to get to corner and edge menu buttons, especially on smaller screens.
What is the phone you're using ?
Maybe goolge it, and see what brightness it is, should be able to find a 'nits' rating, and maybe compare to something else that might be something to purchase mid to long term.
Eg. my iphone 6 is up to 600 nits
The ipad
mini 4 is 450 nits, but it is a lot brighter looking / much easier to see than the phone, plus it's got much more room for displays like histogram, attitude display, map, etc.
Still fits in the arms, which is handy.
If you can't get a larger device for any reason, I usually just try and fly in the shade, tree, broad brim hat and back to sun etc.
People here rave about the
Crystal Sky, which is 1000 nits to the larger one at 2000 nits.
The
DJI smart controller is also 1000 nits.
They would be awesomely bright for sure, but not a light (no pun intended) investment.