It sets pattern validation key if input field data does not match a RegularExpression that is bind to ng-pattern(re).In this correct form of mobile number show in placeholder.
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.2/angular.min.js"></script>
</head>
<body ng-app="app">
<div ng-controller="controllerName">
<ng-form name="mobileForm">
Mobile:
<input type="text" ng-model="mobile" name="mobile" placeholder="+91-9855514371" ng-pattern="re" />
<br />
<span ng-show="mobileForm.mobile.$error.pattern" style="color:red">Mobile number should be in valid formate.</span>
</ng-form>
</div>
<script>
var app = angular.module("app", []);
app.controller('controllerName', ['$scope', function ($scope) {
$scope.re = /^(\+\91{1,2}[- ])\d{10}$/;
}]);
</script>
</body>
</html>
