The attachable property Phone was not found in type OnIdiom

I started getting this XAML warning after the latest XF version on VS 2017 v15.7.1.
This is the code in App.xaml:

<OnIdiom x:Key="largeFontSize"  x:TypeArguments="x:Double">
    <OnIdiom.Phone>
        <OnPlatform x:TypeArguments="x:Double" iOS="23" Android="23"  />
    </OnIdiom.Phone>
    <OnIdiom.Tablet>
        <OnPlatform x:TypeArguments="x:Double" iOS="28" Android="28"  />
    </OnIdiom.Tablet>
</OnIdiom>

The attachable property Phone was not found in type OnIdiom.

And I also get another warning here:

<Thickness x:Key="pageContentPadding">10,0,10,0</Thickness>

The type 'Thickness' does not support direct content.

I've used these styles since the beginning of the app with no warning, until now.
How should I change them now?