Employer wants me to sign new cell phone policy

I am in ontario, I am just wondering if it is legal for an employer to do this?

They want us to sign a new policy stating we cannot use cell phones during work hours (I understand breaks and lunch only) and that they can take your phone during work hours?? Can they legally take your private property?

How can I fight this? I will sign it but I do not comply with them taking my personal property I have incase of emergencies with my kids .... I also do not want to lose my job though if I do not sign.