This compact smartphone gaming controller works equally well in portrait configuration too - Yanko Design
topp Gaming Smartphone Controller 'Remus' with up to 12 Hours Running Time and Individually Adjustable Button Assignment, Black: Amazon.de: PC & Video Games
Nacon's MG-X Pro smartphone gamepad is comfortable but a little too basic
GameSir X2 Turns Your Smartphone into a Nintendo Switch-like Console | Beebom
Smartphone-Controller: Fünf Modelle für Spielspaß unterwegs - COMPUTER BILD
Grefay Mobile Game Controller Smartphone Pubg Gamepad Simplified Portable Universal Mobile Controller for All iOS iPhone Smartphone(Without Joystick) : Amazon.co.uk: Electronics & Photo
Razer Kishi for Android - Smartphone Gaming Controller (USB-C Connection, Ergonomic Design, Individual Fit for Mobile Phones, Analog Stick, Ultra Low Latency) Black : Amazon.co.uk: Electronics & Photo
Guidemaster: Game controllers to turn your smartphone into a mobile gaming machine | Ars Technica