PBR radios are designed and built to works for years in all types of environment, are more rugged in construction than mobile phones and have a higher power output.
Mobile phones offer a wide area of coverage and the ability to contact individual people.
Every time you do this is costs you money. And with contact phones you also pay a monthly service charge. Two way radios offer instant communication with any one or all of your own site personnel. There are no call costs, no service charges. If you buy PMR446 radios there is no yearly licence to pay.