Yes, it is possible for a phenomenon known as "cross-talk" to occur during a phone call, where one person hears the voice of a third person. This can happen due to technical issues or malfunctions in the phone system or network.
Cross-talk can occur in analog phone systems, although it's less common in modern digital and cellular networks, which have more sophisticated technology to prevent such occurrences. In analog systems, the electrical signals carrying the audio of multiple phone conversations can sometimes interfere with each other, leading to cross-talk.
In digital networks, cross-talk is less likely to happen due to the way data is transmitted and separated into discrete channels. However, it is still possible for other technical issues to cause audio problems during a call, such as echo, dropped packets, or voice distortion, which could give the impression of hearing a third person's voice.
If you ever experience this kind of issue during a phone call, it's usually a temporary glitch in the system. Hanging up and redialing the call should usually resolve the problem. If the issue persists, it might be worth contacting your phone service provider to investigate and address the problem.