Following event handler should do the needful:
$('[name=mobilePhone]').on('keyup', function(e){
var enteredNumberStr=this.$('[name=mobilePhone]').val(),
//Filter only numbers from the input
cleanedStr = (enteredNumberStr).replace(/\D/g, ''),
inputLength=cleanedStr.length,
formattedNumber=cleanedStr;
if(inputLength>3 && inputLength<7) {
formattedNumber= cleanedStr.substr(0,3) + '-' + cleanedStr.substr(3,inputLength-1) ;
}else if (inputLength>=7 && inputLength<10) {
formattedNumber= cleanedStr.substr(0,3) + '-' + cleanedStr.substr(3,3) + '-' + cleanedStr.substr(6,inputLength-1);
}else if(inputLength>=10) {
formattedNumber= cleanedStr.substr(0,3) + '-' + cleanedStr.substr(3,3) + '-' + cleanedStr.substr(6,inputLength-1);
}
console.log(formattedNumber);
this.$('[name=mobilePhone]').val(formattedNumber);
});