Equivalent of phpMyAdmin for MSSQL?
There is MyLittleAdmin that we use. I find it strange that it's not been mentioned here. We've used it for years and I think our developers find it works well for them. I think it's crazy that there's not a official web based tool like phpMyadmin for MSSQL. I don't want to give our developers access to our production SQL Servers so a web based solution is ideal for us.
There's no default web interface like phpMyAdmin. Typically you wouldn't want to expose your Microsoft SQL Servers to the public net. You would normally connect via VPN then use SQL Server Management Studio to connect.
The web interfaces that you found will probably do the trick, but without providing access to some of the newer features. If you are just looking for basic functionality those will work just fine. The nice thing about SQL Server is that anything you can do in SSMS you can do in T/SQL so if the web interface you have doesn't provide functionality you can still manage and use those features using T/SQL.