摩肩接踵

lit. rubbing shoulders and following in each other's footsteps / a thronging crowd

to rub

shoulder / to shoulder (responsibilities etc)

to receive / to answer (the phone) / to meet or welcome sb / to connect / to catch / to join / to extend / to take one's turn on duty / to take over for sb

to follow on sb's heels

to arrive / to follow / heel