Currently AMQ broker's manual states that it is not possible to expands Broker's PVC once it has been created [1].
OpenShift cluster Web console offers an option of expanding a PVC. The broker's operator should allow such operation.
Alternatively, if such option is not possible to be automated, we should document and support a manual option to expand PVC. This is required in case a broker runs out of disk space and its PVC size needs to be increased.

I have tested a manual process of expanding PVC via cluster's web console and it worked for me.

[1] https://access.redhat.com/documentation/en-us/red_hat_amq_broker/7.10/html/deploying_amq_broker_on_openshift/assembly-br-configuring-operator-based-deployments_broker-ocp#proc-br-configuring-broker-storage-size_broker-ocp