If you have any fear of someone at a studio claiming that they wrote your song, then you should register the copyright in your musical composition sooner than later. Why wait until you have a finished sound recording? For a $35.00 dollar fee to the Copyright Office you can register the copyright in the words and music of your composition by uploading a copy of the telephone recording. The registration (and proof of ownership) would be effective as of the day the copyright office receives the payment, electronic application, and uploaded copy. That could be as soon as it takes for you to actually do that after reading this answer.
Hire an attorney. This is you umpteenth question here. You are done with the free, now hire a lawyer and start paying for your advice. Avvo is not a recipe for avoiding lawyers, it is a means to find one. You are very foolish to think otherwise.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.