Hi, since the new version of ESX essentialmode was removed and now you need to change some things server.lua

Change this

AddEventHandler('es:playerLoaded',function(source)
local sourcePlayer = tonumber(source)
local identifier = getPlayerID(source)
getOrGeneratePhoneNumber(sourcePlayer, identifier, function (myPhoneNumber)

TriggerClientEvent("gcPhone:myPhoneNumber", sourcePlayer, myPhoneNumber)
TriggerClientEvent("gcPhone:contactList", sourcePlayer, getContacts(identifier))
TriggerClientEvent("gcPhone:allMessage", sourcePlayer, getMessages(identifier)) end) end)

To This 

AddEventHandler('esx:playerLoaded', function(playerId, xPlayer)
local sourcePlayer = tonumber(xPlayer.source)
 local identifier = xPlayer.identifier 
getOrGeneratePhoneNumber(sourcePlayer, identifier, function (myPhoneNumber)

TriggerClientEvent("gcPhone:myPhoneNumber", sourcePlayer, myPhoneNumber)
TriggerClientEvent("gcPhone:contactList", sourcePlayer, getContacts(identifier))
TriggerClientEvent("gcPhone:allMessage", sourcePlayer, getMessages(identifier)) end) end)

I Hope, this will fix your issue on your server.