How reliable are VoIP phones during peak internet traffic?

Modern fibre broadband is well capable of handling the sorts of VoIP phone traffic a small business is likely to be dealing with. VoIP calls take up a tiny amount of data bandwith, so in most cases, reliability is rock solid. For a smaller business, if you're using the same internect connection for voice and data, ensure that the QoS (Quality of Service) is set-up on your router so that it allows for there to be some bandwidth always available to make calls if your users are likely to be using up that bandwidth which could impact your business calls.

Larger businesses with hundreds of phone users would likely have separate dedicated VoIP packages to handle calls. Larger businesses still, would likely also have a failsafe network connection to back that up.