Is this a properly formatted POST request? - php

Question

Is the below code a properly formatted POST request? It seems as those the entire contents are being passed via the URI and not via POST. I only have a very primitive understanding of PHP and URL requests in general so the server-side code has been included below as well.
I noticed this was an issue while attempting to upload base64 encoded images (as demonstrated below) to the server. Upon submitting the request, the server would return an error stating the that URI exceeds the maximum length, which leads me to believe that this isn't a proper approach to submitting a POST request. The entire process works if the image is only 10x10px, but that isn't going to do the trick and the main priority here is understanding the correct approach.
What is the proper approach to submitting a POST request, similar to the below example?
How can the POST data be received by the server and will the JSON need slashed stripped if it is properly submitted via POST?
Swift
if let imageData = UIImagePNGRepresentation(self.image!) {
let encodedImage = imageData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions(rawValue: 0))
let dict = ["barcode":self.barcode, "imageData":encodedImage]
let json = JSONStringify(dict, prettyPrinted: false)
let jsonEncoded = CFURLCreateStringByAddingPercentEscapes(
nil, json, nil, "!*'();:#&=+$,/?%#[]", CFStringBuiltInEncodings.UTF8.rawValue)
let server:String = GlobalVars.serverAddress
let phpFile:String = "/php/Inventory/UpdateItemImage.php"
let baseURL = NSURL(string: "\(server)\(phpFile)")
let url = NSURL(string: "?json=\(jsonEncoded)", relativeToURL: baseURL)
let cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringLocalCacheData
let request = NSMutableURLRequest(URL: url!, cachePolicy: cachePolicy, timeoutInterval: 10.0)
request.HTTPMethod = "POST"
let dataString = ""
let requestBodyData = (dataString as NSString).dataUsingEncoding(NSUTF8StringEncoding)
request.HTTPBody = requestBodyData
var response: NSURLResponse? = nil
do {
let reply = try NSURLConnection.sendSynchronousRequest(request, returningResponse:&response)
return true
} catch {
return false
}
}
PHP
<?php
// Setup DB connection etc..
//..
//Define passed variables
$json = $_GET['json'];
$json = stripslashes($json);
$fieldArray = json_decode($json);
$barcode = $fieldArray->{"barcode"};
$imageData = $fieldArray->{"imageData"};
// etc....
?>