Hmmm... Why would he say that he usually uses Facebook or Gumtree but wanted to try eBay if he has feedback and is not new to eBay? And buyers can only have positive feedback by the way (or is he also a seller)? Strange he would ask to send the item and pay after inspection (this is not even allowed on eBay), but then he did pay, right? 

Yes, that message about funds on hold is from eBay and applies to all sellers who don't sell regularly, so that is true, but the buyer does sound a bit suspicious to me. 

I am not a seller, so I will let other sellers give you some advice based on experience,

Just make sure if you do send the item that it has a tracking number. Take a pic of the serial number of the phone too, just in case the buyer is a scammer, claims the phone is broken and then sends you back his phone...