As per gsma doc for volte service description and implementation guidelines-
3.2 VoLTE Basic Call Flows
The VoLTE basic call flows are in accordance with 3GPP specifications for E-UTRAN/EPC,
IMS, and PCC. Please refer to 3GPP TS 23.401 , 3GPP TS 23.228 , and 3GPP TS
23.203  respectively for further detailed information.
3gpp spec 23.401:
184.108.40.206 IMS voice over PS Session Supported Indication
The serving PLMN shall send an indication toward the UE during the Attach procedure and Tracking Area Update
procedures if an IMS voice over PS session is supported. The serving PLMN uses this indicator to indicate to the UE
whether it can expect a successful IMS voice over PS session according to TS 22.173  with a bearer that supports
Conversational Voice as specified in TS 23.203 . A UE with "IMS voice over PS" voice capability should take this
indication into account when establishing voice over PS sessions (as specified in TS 23.221 ) as well as when
determining whether to deactivate the special handling of ISR locally (as detailed in clause 220.127.116.11)
As per these specs , volte call pkts should go with qci 1 bearer.