Admob Ads Do No Display in Phones Only Tablets?

My game does not display ads when I install it in phones, they only show up in tablets.

Devices where ads are displayed:

Device: Motorola Xoom

Android Version: 4.1.2

Device: Samsung Galaxy Tab 3 (10inch)

Android Version: 4.2.2

Devices where ads are not displayed:

Device: Samsung Galaxy S5

Android Version: 4.4.2

Device: HTC One V

Android Version: 4.0.3

In the devices where the ads do not display: there is occasionally a completely black rectangle where the ad should be as if I had set the parameter testMode = true. If i do set the parameter testMode to true the black rectangle (test ad) is always there.

Corona Simulator: 2014.2189 (2014.3.6)

main.lua code:

local ads = require "ads" local appID = "ca-app-pub-xxxxxxxxxx/xxxxxxxxxx" local provider = "admob" ads.init(provider, appID) ads.show("banner",{x=display.contentWidth/2,y=0,interval=45,appId = appID})

Relevant build.settings code

plugins = {   --key is the name passed to the Lua "require()"   ["CoronaProvider.gameNetwork.google"] =   {      --required!      publisherId = "com.coronalabs"   },   ["CoronaProvider.ads.admob"] = {    publisherId = "com.coronalabs",    supportedPlatforms = { ["android"] = true }   } }, androidPermissions = {   "android.permission.INTERNET",   "android.permission.ACCESS\_NETWORK\_STATE",   "android.permission.READ\_PHONE\_STATE"   }

Thanks for you help in advance.