How do I phrase a data availability statement for data with restricted access?

First check if the journal/publisher have specific requirements regarding the form and phrasing of your data availability statement. Many provide their own templates that you can/should use or adapt, see for example this list from Taylor & Frances:

• Writing a data availability statement - Author Services (taylorandfrancis.com)

If data cannot be published openly, the data availability statement should generally include the reasons for this and information about how/where data can be requested. Below we provide two examples based on solutions we offer at SLU. The reason for keeping data closed may of course vary so make sure you adapt for your specific case. Also remember to check with the journal for compliance with their guidelines.

If you have deposited data with the Swedish National Data Service
"The data that support the findings of this study are not openly available due to their containing information that could compromise the privacy of research participants. Data can be requested from the Swedish National Data Service. A description of the data and information about how to request them are available at [DOI to entry in the SND Catalogue]."

If you have published a data description in the Swedish National Data Service research data catalogue with a link to restricted data in the SLU archive, you can either use the above example and point directly to the SLU archive, or point to the description in the SND catalogue:

"The data that support the findings of this study are not openly available due to their containing information that could compromise the privacy of research participants. Data can be requested from the Swedish University of Agricultural Sciences archive. A description of the data and information about how to request them are available in the Swedish National Data Service at [URL to catalogue entry in SND]."