Look for RGB led strips that use the WS2812B chip. These style of strips allow you to individually control each led. Via your software you would group the leds into banks or zones.
Here is a local supplier to me, but I have seen these strips on Banggood for less than $40. Get a waterproof version. https://core-electronics.com.au/5m-rgb- ... proof.html
Shop around these things are as common as anything, quality varies greatly as does price. You can drive these strips directly from a RPI GPIO pin. There are a number of libraries that support the WS2812.
I would also source some of the purpose made rigid plastic tube that the strip can slide into for more protection.
As for the software. To avoid writing a mobile app, I would setup a basic web server on the RPI, with your control buttons there. Connect to the webserver from the phone either by WiFi or IP Over Bluetooth.