I'm not having any experience with Digital Ocean, but I'm hearing lots of good reviews with their newly launched https://www.digitalocean.com/products/app-platform/
Most of the hosts provide a DB tool like phpMyAdmin(or similar) to manage the databases.
But in this case, after the deployment of a PHP app from a Github repository, how can a user manage the DB of that app. Do they provide a CLI/GUI?
A quick search looks like you are given a connection string. https://www.digitalocean.com/docs/app-platform/how-to/manage-databases/
You can use this connection string to manage your database either through a CLI or use a GUI and input the connection string.