I had a similar situation a few years ago - and it was a pain to correct.
I called a hotel to reserve a room for business travel. While I was on the line, I also reserved a room for a coworker who was traveling with me. I held the reservation on my card since my coworker wasn't around at the time. When we checked it, I made sure they switched the reservation to his card - or so I thought. When I got my statement, I'd been hit with his charges and mine. We called the hotel and sorted it out - but that wasn't the end of it. Now I had a debit in one month and a credit in the following month. In order to avoid refund scams such as an employee reporting a charged expense and then getting a refund resulting in a net credit on the card, employees have to reconcile credits to debits so that my employer receives any refunds due. I had to submit receipts and written commentary to prove the original charge was a mistake, that I never filed an expense claim for the original debit, and that the credit negated that original charge.
I don't know your company policy, but this might not be as simple as returning and repurchasing the phone depending on your employer's policy. It's probably best to say "mea culpa" and show that you've taken actions to correct your mistake. And then do something to make sure you never do it again- put a piece of orange tape on the company card or whatever else you need to do. As for me, it's easy... the only AMEX is my wallet is my company card. My personal card is a VISA which is a completely different color, so I'll never make the mistake of confusing the 2.
Good luck.
Sam