Send little text messages to let him know you're thinking of him. Send pictures of what you're doing so he feels connected.
Text, video chat, voice calls/notes, send pictures
My husband and I would do video calls, texts, letters, I would send care packages
You can still call, send voice messages, text. Ask about his day. He'll see your messages when he can. That way he has that reassurance you are thinking about him and miss him.