Option A: Upgrade to Portal for ArcGIS 10.3.
OR
Option B: Navigate to the REST endpoint of the Portal for ArcGIS hosted feature service.
1. Click Create Replica, provide the required parameters, and select Data Format as 'JSON'. Once the Create Replica operation completes, a URL is received.
2. Access that URL to download the JSON file.
3. Use ArcMap conversion tools to convert the JSON file to a feature class.