how to create php web app with ARM template

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I use the following arm template to create php web app, but after I deploy the template successfully, I also can see the default language is .Net. How to fix it.
The template json is as below
```
{
"apiVersion": "2018-11-01",
"name": "[concat(parameters('webSiteName'),copyIndex(1))]",
"type": "Microsoft.Web/sites",
"location": "[resourceGroup().location]",
"copy": {
"name": "webloop",
"count": 2
},
"identity": {
"type": "SystemAssigned"
},
"dependsOn": [
"[concat(variables('targetResourceId'),copyIndex(1))]",
"[resourceId('Microsoft.Storage/storageAccounts', parameters('storageAccountName'))]"
],
"tags": {
"project": "zdemo"
},
"properties": {
"name": "[concat(parameters('webSiteName'),copyIndex(1))]",
"serverFarmId": "[concat(variables('targetResourceId'),copyIndex(1))]",
"siteConfig": {
"phpVersion": "7.3",
"use32BitWorkerProcess": false,
"connectionStrings": [
{
"name": "connstr",
"connectionString": "[concat('DefaultEndpointsProtocol=https;AccountName=', parameters('storageAccountName'), ';AccountKey=', listKeys(resourceId('Microsoft.Storage/storageAccounts', parameters('storageAccountName')), '2015-05-01-preview').key1,';EndpointSuffix=core.windows.net')]",
"type": "Custom"
}
]
}
}
}
```

---
#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 583b2ab0-b032-7fa9-d21f-5203284bd68c
* Version Independent ID: 1e1b0a76-476a-2e71-8eae-837658840081
* Content: [Azure Resource Manager template samples - App Service](https://docs.microsoft.com/en-us/azure/app-service/samples-resource-manager-templates)
* Content Source: [articles/app-service/samples-resource-manager-templates.md](https://github.com/Microsoft/azure-docs/blob/master/articles/app-service/samples-resource-manager-templates.md)
* Service: **app-service**
* GitHub Login: @tfitzmac
* Microsoft Alias: **tomfitz**

Start with articles/app-service/samples-resource-manager-templates.md and the provided Microsoft.Web/sites resource, especially siteConfig.phpVersion. Compare the sample's App Service configuration with the deployed result; done means a reproducible template configuration that creates the PHP app with PHP as its runtime rather than the reported .NET default.

Written by the indexing model from the issue text.