Is the call to prayer (adhan) obligatory, or is it sufficient to just say the iqama (call to commence prayer) when praying in congregation in a workplace prayer room, given that it is difficult to go to the nearby mosque due to the nature of the work?

Congregational prayer is obligatory in the mosque, but if going to the mosque would compromise the public interest or lead to harm, then there is no objection to praying in congregation at the workplace. The Adhan (definition) (call to prayer) and Iqamah (definition) (second call to prayer, signaling the start of prayer) are communal obligations (fard kifaya). If the Adhan is called in a place where the people of that place can hear it, that suffices. The Adhan is not obligatory for every single congregation; rather, the Adhan from a nearby mosque is sufficient. As for the Iqamah, you should perform it to inform those present [that the prayer is about to begin]. It is preferable to perform the Adhan to gain reward, but if you limit yourselves to the Iqamah, there is no harm.