Please, please, PLEASE don't store user's passwords in plaintext on the backend...
If the physical security of the phone is your security, however, this seems like a reasonable level of trust.
There are many apps, like mine, that have non-sensitive data that just needs an account for persistence or extra-app activity.
You could adjust this to require the current password instead of showing it, but in my case that's an unnecessary level of effort. You could still get by with two input fields, I think.
The app is stored un-hashed and un-salted in the app, but if someone gets access to your phone, your powerlifting log is the least of your worries.