I just don't understand him.

Hi Guys 👋🏻 I'm new here and need help to understand a guy I'm interested in so please help if you can.
There's a guy at work and to cut a long story short we're both single and it's pretty obvious that we have feelings for each other but nothing's been said directly. He seems to come forward but then backs off so I asked him if he'd like my number. Anyway his response was 'what for?' Which I really wasn't expecting. He wasn't being mean or harsh and he clearly likes me so why not just say ok and take it?
Any advice please?

Can you give us examples of why you think he likes you as well? It is a rather strange response.