Answer:
I tried it as well and the option is greyed out. It seems like some or all texture packs are not supported on bedrock mobile. This could be due to performance issues, or compatibility. I'm not fully familiar with bedrock mobile, but on bedrock desktop I had no issues.
Descending.
Alphabetical order is from A-Z.
Ascending order is from A-Z.
Descending order is from Z-A.
Hope this helps!
A computer uses BIT. Hope this helps