Finish the application and submit in your notes that the web address is bogus (input google.com or something) and that you are in the process of building a site to ad. I also have used my Linkedin profile URL, and even blogs sites before. It shouldn't matter as your application should state that you're running pay per call offers with call only ads. Affiliate managers know what that means for websites.
Please see also https://kallzu.zendesk.com/hc/en-us/articles/212569145-How-Do-I-Answer-Application-Questions-From-Affiliate-Networks-