ResponsiveUI.xaml

<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             xmlns:local="clr-namespace:GridSample" 
             x:Class="GridSample.GridSamplePage">
    
    <Grid Padding="20" VerticalOptions="CenterAndExpand">
      <Grid.RowDefinitions>
         <RowDefinition Height="40" />
         <RowDefinition Height="40" />
         <RowDefinition Height="40" />
         <RowDefinition Height="40" />
       </Grid.RowDefinitions>
        
      <Grid.ColumnDefinitions>
        <ColumnDefinition Width="5*" />
        <ColumnDefinition Width="5*" />
      </Grid.ColumnDefinitions>

     <Entry Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" Placeholder="UserName" HorizontalOptions="FillAndExpand"/>
     <Entry Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" Placeholder="Password"  HorizontalOptions="FillAndExpand"/>
     <Entry Grid.Row="2" Grid.Column="0" Placeholder="NickName"  HorizontalOptions="FillAndExpand"/>
     <Entry Grid.Row="2" Grid.Column="1" Placeholder="Phone"  HorizontalOptions="FillAndExpand"/>
     <Button Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2"  HorizontalOptions="FillAndExpand" Text="Register" TextColor="White" BackgroundColor="Black"/>
    </Grid>
</ContentPage>