See here: Using obsidian URI - Obsidian Help
That help page does not mention Android, for some reason, but I can confirm that the link on that page, when I follow it from my browser on my Android phone, opens Obsidian.
So, if you follow the instructions at the bottom of that page to specify a particular vault, you should be able to open a specific vault from the address bar of a web browser on your phone.
I’m not really sure how you could add the vault’s URI to your homescreen, though, because to do that, typically something would have to load in your browser, so that your browser recognizes it as an address, which it won’t do, since the link will take you straight to the Obsidian app.
I found this page on working around that problem. It’s a bit old but it may still work: 6.0 marshmallow - How can I edit the URL of a home screen bookmark? - Android Enthusiasts Stack Exchange