My employer has just signed up to get new phones, and I am being told that I will get one, which I do not want as I already have a phone. I was informed yesterday that I will be paying the monthly fee for the phone. Can I be forced to take a corporate phone, that is rarely used by other techs and be made to pay for it?

Employer making me pay for corporate cell phone.
Answers
Does your employer reimburse you anything (even partially) for using your current personal cell phone for business purposes?
See this thread too:
https://www.proformative.com/questions/what-usual-customary-reimbursement-use-personal-cell-phone-business
No, he does not.
I'd talk with your fellow technicians to see how they feel, then consider discussing with your HR leader. Maybe also find out who knows a labor lawyer skilled in your state's legal framework.
Ok, thank you.
This may vary by state but generally the employer cannot deduct anything from your paycheck without your written approval. (Except for the obvious- taxes and court ordered garnishments)
Well, this is being deducted from my bonus.
How much of this is documented in company emails or other documents, that the bonuses will be reduced? I would suggest you print out anything and everything that shows the company's intent/policy/decision.
California Labor Code section 2802 requires an employer to:
“indemnify his or her employee for all necessary expenditures or losses incurred by the employee in direct consequence of the discharge of his or her duties, or of his or her obedience to the directions of the employer.”
Consequently (my interpretation), if the discharge of his/her duties (employee) requires the use of a cell phone, then the employer is required to shoulder the expense....NOT the employee.
There have been several LAW FIRM interpretations of various court decisions on lawsuits regarding the cell phone (personal or corporate) use/reimbursements. Google it. You may also try keywords "BYOD expenses".
http://www.pillsburylaw.com/siteFiles/Publications/Alert20140903LitigationCourtRequiresEmployertoReimburseEmployees.pdf
http://sebastianmillerlaw.com/remote-work-expenses-and-labor-code-section-2802/
I even found a LinkedIn post about the subject.... https://www.linkedin.com/pulse/personal-cell-phones-work-five-lessons-employers-should-zaller
As a P.S., when you think about it there are a lot of "accepted" business practices that should apply (I find unethical or at the very least, predatory)....to include making employees pay for uniforms, etc.
Don't even get me started with the "low wage + tips" compensation that is prevalent in the hospitality/restaurant industry. But I digress.
My general rule as I said is....the employer is responsible for providing ALL the resources an employee needs in the discharge of his/her duties.