No, you cannot make payments directly from your Gsave account, you need to transfer your money from your GSave by CIMB account or #MySaveUp by BPI account to GCash Wallet to pay for your GCash transactions.
To learn how to do this, visit How do I transfer money from my GSave by CIMB account to my GCash Wallet? How do I transfer money from my #MySaveUp by BPI account to my GCash Wallet?