As per Virgin mobile website its state's
You’ll need one of these devices to use 4G Calling:
Apple: iPhone SE, iPhone 6, 6 Plus, 6S, 6S Plus, iPhone 7, 7 Plus, iPhone 8, 8 Plus, iPhone X, XS, XS Max, XR, iPhone 11, 11 Pro, 11 Pro Max, iPhone SE2, iPhone 12, 12 Pro, 12 Pro Max and 12 Mini
Samsung: Galaxy S10, S10+, S10e, Galaxy S20 Ultra 5G, S20 FE, S20+ 5G, Galaxy A51, A32 5G, A42 5G, A40, A41, A50, A12, A21s, A52 5G, Note 10+, Note 10+ 5G, Note 20 5G and Note 20 Ultra 5G.
Huawei: P40
All of these devices support 4G Calling if they are bought directly from us. If you are using a device that was bought from another network, or SIM free, we cannot guarantee that it will support our 4G Calling service. If your supported device doesn’t have the 4G Calling option available, make sure you have updated the software to the latest version and reboot your device.
This many be of help for you.
Joe