Ended up needing to use XML for this, which is disappointing. Phone number restrictions should be a native feature in Enterprise
XML:
<characteristic uuid="29888503-64ce-4d3c-9f80-7d4b1876fd48" type="com.airwatch.android.androidwork.samsung.restrictions" target="2">
<!--Add phone restrictions below in the appropriate parameter areas -->
<parm name="outGoingCallRestrictionAllowNumber" value="xxxxxxxxxx,xxxxxxxxxx" />
<parm name="inComingCallRestrictionAllowNumber" value="xxxxxxxxxx,xxxxxxxxxx" />
<parm name="outGoingSMSRestrictionAllowNumber" value="xxxxxxxxxx,xxxxxxxxxx" />
<parm name="outGoingCallRestrictionAllowStartingWith" value="xxxxxx.*,xxxxxx.*" />
<parm name="inComingCallRestrictionAllowStartingWith" value="xxxxxx.*,xxxxxx.*" />
<!--Do not add phone restrictions below this line -->
</characteristic>