I can't send funds from the app on my phone too. Yes, i have a phrase that includes 12 words.
Name of file is "electrum-private-keys.json".
With the 12 words you can just import your funds to another wallet
It may be a bug or some incompatibility with the phone app.
Download on desktop, from Electrum.org
Then click"existing wallet" "I have seed phrase"
Your funds will be there.