allTemplates.html

<template name="mainTemplate">
  {{#if isPhone}}
    {{> mobileTemplatePartOne}}
  {{else}}
    {{> desktopTemplate}}
  {{/if}}
</template>
	
<template name="mobileTemplatePartOne">
  //first half of stuff
  <a href="{{ pathFor 'mobileTemplatePartTwo' }}">Second Part</a>
</template>
	
<template name="mobileTemplatePartTwo">
  //second half of stuff
</template>
	
  <template name="desktopTemplate">
    //all the stuff
  </template>

routes.js

Router.map(function() {
  this.route('mainTemplate', {
    path: '/main'
  });
	
  this.route('mobileTemplatePartTwo', {
    path: '/main/parttwo',
    action: function() {
    if (Meteor.device.isPhone() == false) {
        Router.go('/main');
      }
    else {
        this.render();
      }
    }
  });
});