How do we claim the expenses for working from home during COVID? My employer did not provide any reimbursement for my cell phone, computer, office space or electricity

Sorry---W-2 employees cannot deduct expenses for working from home.  Job-related expenses were eliminated as a deduction for W-2 employees by the tax laws that changed for 2018 and beyond.  Your state tax laws might be different.

https://ttlc.intuit.com/questions/4482873-which-federal-tax-deductions-have-been-suspended-by-tax-reform