You can click on the "Task action" icon on the upper right corner of the first of each project. It's the one with the crossed wrench and pencil. Click on the "Sort by name" option to sort your tasks alphabetically.
Is it possibel to do this in the phone or tablet app?
I've found the sort tool in the browser version - as you decribe here.
But i cant find the function in the app..?
Unfortunately, it's indeed not available in our mobile apps yet, but we'll consider adding it to these platforms in future updates :-)