Lightroom Mobile requires a CC subscription plan:
Lightroom mobile is included as part of the following Creative Cloud membership plans:
If you have access to Lightroom 5 via your Creative Cloud membership, then you have access to Lightroom mobile.
Since Lightroom mobile is a service, it is available only via membership plans. Lightroom 5 perpetual license does not include access to Lightroom mobile.
Without a CC subscription I believe you only have a 30-day trial period:
If you have perpetual license for Lightroom, Lightroom mobile gives you the opportunity to use Lightroom mobile for a 30 day trial. If you use the trial, you can get assistance through our forums: