Cisco IP phones and their IP addresses

I am having a big issue with the IP phones.

we have 2 VLANs, which are the Data and the Voice VLANs.

the IP phones suddenly stopped registering to the CUCM, I put a static IP address on the IP phone it worked fine, I did another troubleshooting step, which is to remove the voice VLAN configuration on the port where the IP phone is connected so the only configured VLAN is the DATA.after that I can see that the phone directly got an IP address from the DHCP server which is the core switch.

the only difference between the DHCP pools is the option 150 configured on the voice VLAN pool.

any help with this.