What protocol allows a computer to connect to the Internet over a phone line?

Point-to-Point Protocol (PPP) is specifically designed for establishing a direct connection between two nodes, allowing for the transmission of data over phone lines and other types of network connections. It facilitates the connection of computers to the internet by enabling communication over dial-up connections, which use standard telephone lines. PPP is capable of transmitting multiple network layer protocols, providing support for features such as authentication, encryption, and compression.

In contrast, Hypertext Transfer Protocol (HTTP) is a protocol primarily used for transmitting hypertext over the Internet, mainly concerning web page data. File Transfer Protocol (FTP) is intended for transferring files between systems, while Internet Message Access Protocol (IMAP) is designed for retrieving emails from a mail server. These protocols do not serve the function of connecting a computer to the Internet over a phone line, which is why PPP is the most appropriate choice for this question.