Filing on your phone does not determine whether you need to pay. The software version you use is what determines whether you pay to use TurboTax. And the fee to use online TT software is the same whether you e-file it or put in in an envelope and mail it.
Did you choose to have TT fees deducted from your Federal refund? (Remember that if you did that, you also agreed to an extra refund processing fee of $39.99 -- or $44.99 in CA)
How can I see my TurboTax fees?
https://ttlc.intuit.com/questions/2565973-how-do-i-review-my-fees-in-turbotax-online
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**