Yes, to use the Lavalier II with a smartphone or tablet, you need a TRS to TRRS adapter like the RØDE SC4. This is because most mobile devices have a TRRS input, which is not compatible with the Lavalier II's TRS output. For devices with Lightning or USB-C port, you will also need to use a 3.5mm to Lightning/USB-C adaptor.
For a simplified setup with more features and better sound quality, we recommend using the AI-Micro to connect any microphone with a 3.5mm output to your phone or tablet, including the Lavalier II.