Why would he give me his number then not text back?

Well intimidation would be one.

Depends, my job is 'very strict' about not having electronics like phones out, because it breaks compliance. Though that doesn't stop a lot of the people I know from whipping it out.
Sometimes certain phones believe it or not, do have intermittent issues with others.
If he doesn't text you at all he may be playing games. Could be tons of decent excuses but he may just be playing games with you, if a girl did that to me I would be done.
I actually have a friend like that who I rarely talk to anymore lol.

id move on. if a guy can't take the time to even text you back he's not worth it

Well how long exactly has it been since you've texted him? Perhaps he's busy or has things going on. I'd give him a couple days, but I wouldn't hesitate to call him either. Speaking on the phone can be more convenient as to you not really having to wait to get a reply back. If he still doesn't answer wait until he calls or texts you.

I would move on instantly if a guy did that to me unless he had a good excuse.
I don't put up with mind games.