Why is my phone named diagnostic's iphone? Is it really a new phone?

Sorry, Meg. Thought it might be a common thing and someone would tell me it's a common thing and not to worry. This is my fourth iphone and I've never seen this diagnostic name on any of them.

New phone received from the Apple Store yesterday. My old phone stopped holding a charge. This phone was a replacement for a phone I dropped and I got that one new from the Apple Store in January, The Apple guy said something, (can't remember what he said) was burned out and my phone would no longer charge and would have to be replaced. My old phone hadn't been backed up since I received it in January, whoops. I have done nothing to the new phone since I got it yesterday. No one has touched it.

I just thought it odd because the Apple guy kind of made a big deal about it being a new phone, said it was not refurbished, kept stressing it was a brand new phone. Maybe he's used to people freaking out when they have to purchase a new phone to replace a phone they received in January. I was just standing there with my credit card out. All I wanted was a phone that worked. I just hope that it is a new phone since I paid for a new phone.

Thanks for your reply, Meg. I guess as long as it works it doesn't really matter.

Yes, out-of-warranty replacement. Paid $299 plus tax. Thank you for your help.