Welcome to the Apple Support Communities! I see that you're having trouble seeing reviews for an app in the App Store on your iPhone. I always check the reviews before I download a new app, so I know how important it is that they are there for me to read. I would be happy to help!
Is this happening on all apps, or just a certain app that you're wanting to check out? Keep in mind that the reviews start over when a new version of that app gets released, so if it's a fairly new version, there might not be any reviews for that one yet. To see all reviews for ALL versions of the app, you would go to the app's page, tap "Reviews", then tap "All Versions" under "Ratings and Reviews".
Did you know you can also look for apps and read reviews on your computer by going to this page? iTunes Preview - App Store
Please let us know if you have further questions or need clarification.
Take care!