Explorer for ArcGIS (iOS) v17.1.1 labels a field with the Code value instead of Description value when the labels are created on an ArcGIS Server map service within ArcGIS Online.
Turn labels on in ArcMap before publishing map service. Explorer displays Coded Value domain Description as intended.
Create a Query Layer or View in ArcMap. Use the following article to write a SQL statement which explicitly returns a Coded Value domain Description (examples for SQL Server and Oracle only). <a href="http://desktop.arcgis.com/en/arcmap/latest/manage-data/using-sql-with-gdbs/example-resolving-domain-codes-to-description-values.htm" target="_blank">http://desktop.arcgis.com/en/arcmap/latest/manage-data/using-sql-with-gdbs/example-resolving-domain-codes-to-description-values.htm</a>