I would use the usb charger that came with your Sony T2 Ultra phone.
However, the whole purpose of the power bank is to be an alternative power supply/battery for recharging usb devices.
So you would use the powerbank if you find yourself without any other charging options: e.g., Wall outlet, computer with a USB port, Automobile USB charger, etc..
Here is a little guide:
https://www.powerbanksdepot.com/blog/tag/wholesale-power-bank/
Just be sure to read your Sony documentation - look for any warnings, limits, or other guidelines with respect to recharging. Those guidelines take precedence in order to protect your device and any warranties.