In practice, most businesses are simply handling this on a case-by-case basis since COVID is a temporary problem. Most home networks can handle the extra load as long as the employee makes sure that other latency-sensitive traffic, like gaming or video streaming, is kept to a minimum during the hours when they need to talk. If some home routers develop problems, IT staff simply build a queue and handle those one at a time. Sometimes they'll be able to access the router remotely with the employee's permission, sometimes they'll have to walk that employee through configuration steps to fix the problem. Sometimes the employee will just have to live with it unless the company springs for a new router or a higher bandwidth tier from the employee's ISP.
VoIP systems, sometimes called cloud PBXes, can manage all your voice communications from a central web console no matter how many extensions you've got, where your employees are located, or even what devices they're using. Most systems also offer features like video conferencing and team collaboration. Put all that together with subscription-based pricing that's generally much cheaper than an old-fashioned, on-premises PBX, and VoIP remains one of the best communications investments any business can make, especially during the pandemic.

Consider their quality and if the tools you use are performing at a top-notch level. Interactions and tools affect the customer’s overall experience with your business.
Finally, for a minimum monthly cost of $99, you can get Talkroute’s Enterprise virtual phone line plan. Created for large teams with complex needs, this option comes with five phone numbers, unlimited text messages, unlimited extensions, 20 voicemail inboxes, everything offered in the first three tiers, plus dedicated account management and custom integration services.