I have create a custom app and installed in MS teams and it is showing in the app bar next to Teams icon. But when I login to mobile app, unable to see the app.
The Teams mobile clients (iOS and Android) currently don’t support personal apps with static tabs. Depending on the apps set in the policy, apps pinned to the Teams desktop client might not appear in the Teams mobile clients. Personal bots will still appear in Chat on mobile clients.
With the Teams mobile clients, users will see core Teams apps such as Activity, Chat, and Teams, and you can pin some first-party apps from Microsoft, such as Shifts. reference
Larry Jin – Program Manager(Microsoft)mention that we expect in the next couple of months better support for tabs, messaging extensions, and other app capabilities on Teams iOS and Android clients.
This feature currently not supported but is coming! Larry Jin were talking about this in this MS build session 6 May 2019 link