Newly switched to Telus, noticed low voice quality when calling my friends who are on Fido with their VoLTE. Notice the VoLTE toggle switch is gone in Settings > Cellular > Cellular data options > Enable LTE > Voice & data.
I checked my iphone IMEI with telus, says it should be compatible with Telus VoLTE (https://www.telus.com/en/support/article/how-to-use-volte). Contacted tech support but was told it was due to signal strength. I ended up driving up near the tower where 5G is full strength but call was still not HD quality when I test called there.
If your device is supported as you mentioned, and the signal strength is sufficient it should work. Though it's also hit or miss when the other side isn't on VoLTE either. Personally I haven't noticed a huge deal breaker of a difference between VoLTE and regular calls... but if you're up next to the tower, are in a VoLTE-capable LTE coverage area, and it's still not switching you to VoLTE you'll need to reach out to the tech support team when you're at or by the tower so that they can troubleshoot the issue with you.