It's free to download in the App Store and Google Play under the name FreshFlow. After downloading, sign in with the same login details you use for the FreshFlow web app.
Click on the three horizontal lines in the top left corner and then click on the Import contacts section. You'll see contacts from your phone that can be imported.
Tick the contacts you want to import. If you have any tags you want to add to the contacts, you can tick those too and the contacts will be saved with the tags.
Then click Save. The contacts will be saved to the database.