Your phone number is used for 2fa and should be kept hidden and safe by those companies. Just knowing your phone number can't really make someone guess which services you linked it to. 
Well, your phone provider probably knows. And with some effort and a couple of data breach leaks from the sms service these companies use to send 2fa messages one could technically be able to connect the dots, but it seems like too much trouble for the average guy.

I used my phone number for verification for several porn sites, also, I have a google+ and Steam accounts tied to that number. If someone knows my phone number, can they find a link between those, somehow?

Can someone find out which accounts are tied to my phone number?