Here's what happened
Originally the phone box was a power receptacle and the blue box wasn't there.
Look at the short run of old Romex between the phone box and the blue box. That run used to go all the way to the other steel box, but the cable had a problem. So the last guy cut a hole for access and installed the blue box as a splice point. (keep in mind the drywall was installed; he was reaching through.)
Why he moved the socket to the blue box and put a phone box in the old location - I have no idea. It is illegal to put a phone jack there.
Fix it the way they intended
They gave you enough length in the new Romex for the metal boxes to connect to each other - they just didn't have the access to complete the job. I would convert the "phone" box back to a receptacle box, and deprecate the blue old-work box, as the way it's mounted is a compromise and not particularly strong.
- Open up the blue box and remove all wires from it, being careful to remove the newer Romex intact (the short old Romex can just be cut).
- Open up the phone box, remove the phone socket, and finish removing the short old Romex and throw it away.
- Into its hole goes the newer Romex.
- Install a power receptacle where the phone jack had been.
- On the blue box, fit a blank cover plate or convert it to comms use (cable TV, ethernet, phone etc.)
Now the two metal boxes are your receptacle boxes again. They are properly anchored to the joist, so if you are wrestling a stiff plug, there's no worries of tearing the box out of the drywall. Metal boxes don't burn or melt, and can be grounded.
If the wiring is not already grounded, now is the time to retrofit grounds to all the boxes (except the blue one obviously.) In 2014 they greatly relaxed the rules on retrofitting grounds.