Why Classic VHF packet (AX.25 at 1200 baud) sends audio tones through an ordinary FM voice transceiver, so the RF is frequency or phase modulated. FM/PM works well here because it is constant amplitude and immune to amplitude noise, and standard VHF FM rigs are cheap and plentiful. The tones are just AFSK audio fed into the mic input, so the transmitted emission type is the FM (or PM) the radio already produces.
Watch out SSB is the usual choice for weak-signal VHF work and for HF data, and some higher-speed HF packet uses it, but VHF packet gear is built around FM voice radios. PSK modes like PSK31 are separate keyboard modes, not the AX.25 packet standard on 2 meters.
Packet rides on the same 2 meter FM radio you use for repeaters: VHF packet = FM.