Open webhook.lua and at the bottom for the function customphonefunction add the example below in that function and configure to make sure the correct arguments are passing.
TriggerEvent('jpr-phonesystem:server:sendEmail', {
Assunto = data.subject, -- do not change as data.subject is correct.
Conteudo = data.message, -- make sure that this corresponds with the correct argument from above.
Enviado = data.email, -- do not change as data.email is correct.
Destinatario = data.identifier, -- make sure that this corresponds with the correct argument from above.
})