CallParticipantDetail
One additional participant's lifecycle on this call.
- phoneType: string
_number requiredThe number dialed for this participant, in E.164 form.
- joinedType: stringFormat: date-timenullable
_at When this participant came onto the open line, or null if they never did.
- leftType: stringFormat: date-timenullable
_at When this participant left the call, or null while they are on it (or if they never joined).

