I assume that by hotspot you mean using your phone as an internet source (tethering).
This is possible in principle. Since a smartphone is needed to set up the WLAN, there are two ways to set up the connection with a hotspot. The most obvious option is to use a second phone, as the first one has to maintain the hotspot all the time.

The second variant is to first connect the speaker to its home WLAN as normal. Then simply change the SSID and password of your smartphone hotspot so that it is identical to the home WLAN. The speaker will then automatically connect to your smartphone (of course only when you are outside your home WLAN).

I have already used the second option. In my opinion, it is the simpler one, as it is relatively time-consuming to change the Wi-Fi settings of the Google Home. You always have to complete the whole setup.

Theoretically, you could also connect the Google Home Mini to the phone via Bluetooth. But this only works if it is already connected to Wi-Fi. All the voice commands only work via Wi-Fi. Therefore, this is not a solution for on the go.