The code that is commonly used to assign higher priority to VoIP traffic is EF, which stands for Expedited Forwarding. EF is a per-hop behavior (PHB) defined by the Differentiated Services (DiffServ) model for QoS. EF provides low delay, low jitter, and low loss for real-time applications such as VoIP. EF is marked by setting the DSCP value to 101110, which corresponds to decimal 4678. AF31, which stands for Assured Forwarding class 3 low drop probability, is another PHB defined by DiffServ, but it provides lower priority than EF. AF31 is marked by setting the DSCP value to 011010, which corresponds to decimal 2678. DF, which stands for Default Forwarding, is a PHB defined by DiffServ that provides best-effort service for unmarked traffic. DF is marked by setting the DSCP value to 000000, which corresponds to decimal 078. AF11, which stands for Assured Forwarding class 1 low drop probability, is another PHB defined by DiffServ, but it provides lower priority than EF and AF31. AF11 is marked by setting the DSCP value to 001010, which corresponds to decimal 1078.

References: Differentiated services - Wikipedia, Solved: Cisco VoIP Phone traffic marking - Cisco Community