Same here, 6’4" and size 12 or 13 US depending on how they are made. I have a hard time finding shoes that fit well, I seriously feel for OP.

My cousin is 6’8" with size 15, he also has a hard time finding good shoes as well as other clothes.

There’s a company called Unihertz that sells a line of keyboard Android phones similar to the last batch of Blackberry models. I know it’s not slider phones but they are inexpensive.

There is also Planet Computers which makes sliding Qwerty phones but they are expensive.