A Loomo cannot connect with multiple smartphones at the same time. Once a phone connected to a Loomo, the connection requests from other phones will be rejected.
If you want to log in to the Loomo mobile app on another smartphone with the same account you have created before, you will need to disconnect your previous phone from Loomo and then connect to Loomo on the new phone via the Loomo app.
If you want to log into the Loomo app with another/new account, please refer to the FAQ topic: How can other users connect their smartphones to Loomo?