I want to play the audio from youtube videos on outdoor speakers. I understand I could do this with a 4G phone and bluetooth s

[musiconwifi]

How to use wifi to play music on outdoor speakers/

 

[Alabalcho]

Without Wifi, ho do you play music today on these?
It would be much easier with BlueTooth - all you need is a BlueTooth receiver (with audio-out, usually 3.5mm or dual red/white RCA plugs) plugged into the amplifier which powers these speakers.

As for WiFi - you are probably talking about "streaming" from a PC with plenty of music. For this, you would need some media streaming box, it's audio output connected to the amplifier, and controlled remotely from your smartphone.

Specify these details, and let us know your budget.