This can be done a few different ways depending on what you want to accomplish
Apex Classic dashboard with LOCAL connectivity:
You could pick up a TP link travel router, advantage is that it is tiny, smaller than a deck of cards. Set it up using client mode. The travel router will hard wire to your Apex giving you wireless connectivity to it.
The travel router is configured using the SSID and password you have created on your phone/hotspot. Once you have this setup, the tp-link travel router will receive internet from your hotspot tether (same as hooking up a laptop, choose the wireless network you want to connect to (SSID) enter the password, and boom, internet).
Then you will be able to connect to your apex CLASSIC dashboard by connecting to the IP address listed in the network setup on your apex display controller
Apex Classic Dashboard with REMOTE Connectivity:
now... remote connectivity is a different situation
You will still need the TP-LINK router, BUT you will most likely be unable to use the mobile hotspot tether on your phone for remote connectivity because you need to have port forwarding capabilities. To do this you would need to purchase a jetpack hotspot, I am providing the example of Verizons 6620L Jetpack. With this you will remotely connect to the WAN IP of your hotspot and it will forward your connection to your apex. To do this you can buy a Jetpack hotspot from your cell phone provider. See link below, the jetpack MiFi 6620L offers the ability to configure port forwarding. The advantage here is that hotspots (if you have an unlimited plan) are extremely affordable to tack onto your monthly bill and can provide you with constant connectivity remotely and while at home.
If you go this route, you will still configure the TP-Link Travel router the same as listed above, however you will configure the port and IP address listed in your Apex display/controller in the port forwarding on your jetpack. Then when you connect remotely, it will be to the WAN IP address and the port you are configuring. ex: if your WAN IP is 123.123.123.123 and you set it up to port 8800, then your URL to connect to the Apex Classic Dashboard would be 123.123.123.123:8800
With either of these configurations you will be able to use Apex Fusion, however, it would be best to use the jetpack so that fusion does not disconnect every time. You will want your DHCP set to not be auto, and hardset the IP address in your apex. If you do not do this, the Apex could be issued a different IP address every time the hotspot connects which would require your changing the configurations every time.
TP-Link Travel Router:
https://www.amazon.com/TP-Link-Wire...coding=UTF8&psc=1&refRID=5F9A1VE6KKJ60QC49A60
Verizon Hotspot Jetpack:
https://www.verizonwireless.com/internet-devices/jetpack-mifi-6620l/
how to configure port forwarding on the 6620L:
https://www.verizonwireless.com/support/knowledge-base-122749/