If you have a custom Bedrock player skin there is no way to store it in your profile/account to select it again if you switch your device.

If you don't carry your custom skin with you in any way (cloud storage, usb stick,...) you can't use it if you reinstall the app or change your device.

Actual situation:

Everytime you reinstall the App (Android/IOs) or change your device you have to choose your skinfile from the local device or something and upload it.

Expected:

You upload your custom skin once and it is stored in your profile/account in a seperate slot. So you can choose it on every device you log in without uploading it again and again.