How to get back my contacts from Imessage.

Hi everybody,

Having lost my Iphone 6 recently, I wanted to get back some contacts in the meanwhile to get a new phone. To my surprise, when I went to Icloud to get them back, only a few, and old were displayed. I started freaking out, but I notice that when opening Imessage and typing a name, all my contacts were there......
could you please tell me how to extract those contact numbers from imessage and transfer them either to Icloud or Contact (mac application) ? Thanks for your help 🙂

Pierre.