Best VOIP phone system for small businesses

My father, a small business owner who recently transitioned to working from home, is looking to reduce the cost of his landline phone service. He currently pays around $200 per month for two landlines and a toll-free number.

We need a VOIP service that can:

• Port his existing landlines and toll-free number.
• Provide a cordless handset for home use.
• Offer soft phone access through a computer or smartphone app.
• Allow for call forwarding to his cell phone.

I have experience with enterprise-level VOIP systems but am less familiar with smaller business solutions. We're hoping to find a service that can significantly reduce his phone bill to around $50 per month.

What are some recommended VOIP providers that would meet these requirements?