A few things here to bear in mind.
Firstly google does not have to or include every page on your website despite what we would like. They will often deem some pages as too poor content quality or too similar to other pages to add anything to what is already listed for a site. That being said there are a few things to check if you believe these pages are unique and of good quality.
If you view source on a page that is not listed do you see a meta tag that contains nofollow?
If using Wordpress check your htaccess file to see if you have asked google not to crawl these pages.
Next thing to check is to grab a copy of screaming frog https://www.screamingfrog.co.uk/seo-spider/ and crawl your site, do you see the page listed there, if not then something is either blocking it or there are no links to the page internally.
If all the above checks out then in screaming frog check how many inlinks the page in question has, you can try increasing this so you have more internal links pointing to that page which in increase the chance of google visiting the page.
If you don't have any internal links then the page is orphaned which means google would not be able to find it via a normal crawl, In which case the page URL should be put into a sitemap and submitted in search console.
If all the above checks out then let us know and will try and help further.