i am getting the error on account, what is the problem behind this problem i can't understand please verify and send me the right trigger

trigger accountactive on Account (before insert)
{
for(integer i=0;i<trigger.new.size();i++)
{
Account temp=trigger.new[i];
if(temp.phone==null)
{
temp.adderror('must and should enter the phone number(mandetory)');
}
}
}