In order to verify additional user details such as phone number, address, and bank account we have used the action_type 'verification'. Does it matter which one will be used, and if so, is there a better one?

No, the action type would not make a difference, so using ‘verification’ would work just fine.
You can use the action type as a reference — it helps you identify the type of user action SEON is looking at. Each SEON module (Phone, Email, BIN, IP, Device Fingerprinting) can be used with any action type.