My server is a phone now

Then you need to write the server handling code on a background application thread, with perfectly working server sockets.

This only works on wlan, or local network when using bluethooth, but who wants data modem for a server anyway.

With Gemini's compliment,

    import kotlinx.coroutines.Dispatchers
    import kotlinx.coroutines.withContext
    import java.io.BufferedReader
    import java.io.InputStreamReader
    import java.net.ServerSocket
    import java.net.Socket
    import java.net.SocketException

    class AndroidTcpServer {

        private var serverSocket: ServerSocket? = null
        private var isRunning = false

        // Call this function from a CoroutineScope (e.g., lifecycleScope.launch)
        async suspend fun startServer(port: Int = 8080) {
            withContext(Dispatchers.IO) {
                try {
                    serverSocket = ServerSocket(port)
                    isRunning = true
                    
                    // Loop to continuously accept incoming client connections
                    while (isRunning) {
                        val clientSocket = serverSocket?.accept() // Blocks until a client connects
                        
                        if (clientSocket != null) {
                            // Handle each client connection in a separate background routine
                            handleClient(clientSocket)
                        }
                    }
                } catch (e: SocketException) {
                    // Triggered when stopServer() closes the socket
                    println("Server socket closed: ${e.message}")
                } catch (e: Exception) {
                    e.printStackTrace()
                } finally {
                    stopServer()
                }
            }
        }

        private suspend fun handleClient(socket: Socket) {
            withContext(Dispatchers.IO) {
                try {
                    val reader = BufferedReader(InputStreamReader(socket.getInputStream()))
                    val outputStream = socket.getOutputStream()

                    // Read incoming text from client
                    val incomingMessage = reader.readLine()
                    println("Received from client: $incomingMessage")

                    // Send a simple response back to the client
                    val response = "Hello from Android Server!\n"
                    outputStream.write(response.toByteArray())
                    outputStream.flush()

                } catch (e: Exception) {
                    e.printStackTrace()
                } finally {
                    // Always close individual client connections
                    socket.close()
                }
            }
        }

        fun stopServer() {
            isRunning = false
            try {
                serverSocket?.close()
            } catch (e: Exception) {
                e.printStackTrace()
            }
        }
    }

  https://chinese.alibaba.com/product-detail/Mobile-Phone-Group-Control-Equipment-Motherboard-1601460564510.html
  https://www.alibaba.com/product-detail/For-Samsung-Custom-Packaging-OTG-Memory_1601872798649.html
  https://aliexpress.com/item/1005010070778997.html
  https://aliexpress.com/item/1005012481751631.html
  https://www.tiktok.com/@xbus260430425/video/7671530564876258573
  https://www.tiktok.com/@xbus260430425/video/7663701554905582862
  https://www.instagram.com/reel/DP_UrdhEm8R/

I see bunch of multi GPU crypto mining style chassis as well as just USB mass charger styled ones. This is something I just came across randomly so I have no experiences or connections for these, but hope this helps. It's kind of cool looking if it weren't for scams.

edit: note, it's not clear if they come with the phone PCBs or phones are customer supplied. The "boards" mentioned in some of listing seem to imply that it refers to adapter boards for the phones, through subtle wording