Everyone always has their phones on them. Always. Barring some top classified military shit, there is literally no excuse for him not to communicate with you. If he's not getting in touch, he doesn't want to. If he says "Oh sorry, I've been busy" that's code for "you're not on my mind".

I'm not saying he should be communicating with you 24/7, but prolonged stretches of minimal contact means he's breadcrumbing you.

Remember: he's not leaving his phone at home for days or weeks at a time. He could check in, he just doesn't want to.