Why would a guy get nervous by thought of communicating through phone when he talks to you just fine in person?

I talked to this classmate of mine today for a little while, we'd barely talked before and have only attended 3 classes together, but when we'd done talking after our class, he went to the subway and I went to get the bus.

I waited for a little while but I couldn't find a bus so I decided to take the subway. I noticed my classmate was standing outside the station while I was talking on the phone and was going inside the station. He then started following me and as I was buying the ticket, he was just standing a little behind me doing nothing and watching me. So when I finally reached the platform and waited for the train, he came up behind me and said Hi. I was completely startled lol. He then started talking a lot and took the train with me.

The following part creeped me out a bit but then I realised he's a really nice guy so I asked for his number so that we can become friends. When I asked for his number, he seemed a bit nervous, uncomfortable, fidgeted a bit, but he immediately gave it to me in a sec. He also told me to WhatsApp him on this number and that he uses a separate number for calls. I don't know why but after I asked for his number, he seemed totally lost in thoughts (up until then we were talking non-stop) and he became very quiet.
Why would a guy get nervous by thought of communicating through phone when he talks to you just fine in person?
1
Add Opinion