Android stores program data on the removable SD card so one thing you can try is take that out of the phone, insert it into an SD card reader, insert it inside a computer and running file recovery software on that drive.
No, definitely not.
Android makes use of the unix permissions as a security measurement.
The SD card is "free for all". Any application can read/write to it. That would be the last place the wallet file should be stored (and it isn't).
It is stored where it belongs to. In the data directory of the mycelium application owned by the mycelium application user.
@OP:
Don't you have any form of backup? Your mnemonic code?
Did you "just" uninstall myeclium or did you actively delete all mycelium data / wipe your smart phone? Uninstalling the application doesn't necessarily mean the wallet files get deleted. Might be worth to try this out on a second mobile.
Rooting your mobile without wiping the storage would be your best bet. Then you'd be able to access the wallet file and all private key.