Hi Amol,
There is a built-in action in System module to login a user using its User Identifier.

Before using this, you can first check the email and phone number if it exist in User Entity. If it exist, use the User Identifier of the existing record as an input parameter for the Login Server Action.
Also, to validate the entered password, you can use the ValidatePassword of PlatformPasswordUtils to check if the entered password is same with the stored password in User Entity

Hope this helps,
Regards