As PhotoCircle+ provides web access to the subscriber only, you still must join Circles created by others on your mobile device. After you have join on mobile, the Circle will be available when you log in on the web (photocircle.app).
The exception is Circles that are owned by a premium plan Workspace. With PhotoCircle's premium plans, all Circle members, including guest users, can join and access your Circles via the web.
Upgrade to a Nonprofit & Community Premium Plan
Upgrade to a Programs & Groups Premium Plan
Upgrade to a K-12 School Premium Plan