Kenkyusha 新和英大辞典第５版 (GG5)
"太い声 a 「deep ［rich, full］ voice:
Eijiro:
■太い声 : deep tone●deep voice
■太い声で歌う : boom out
■太い声で怒鳴るように言う : boom out
■太い声をしている : have a deep voice

Also, it gets over 200,000 Google hits. Based on that and the references above, I will accept it as a Japanese phrase.
As for the reading, you are right. It should be ふといこえ.

@@ -8,1 +8,1 @@
-<reb>ふといごえ</reb>
+<reb>ふといこえ</reb>

this word looks translated from English word "rich voice" or whatever, not the Japanese word. plus ふといごえ is with 100 percent certainty not correct.

GG5 (声 entry)

Probably OK given GG5's extra glosses.

@@ -12,1 +12,0 @@
-<gloss>deep tone</gloss>
@@ -14,0 +13,2 @@
+<gloss>rich voice</gloss>
+<gloss>full voice</gloss>

It has a good number of Google hits. The principle of a + b probably applies. And, as Rene, states, if you don't know the standard readings for the suffix one should look elsewhere.

However, you do have the following on site:-

太い鉛筆 【ふといえんぴつ】 (n) broad pencil
太い腕 【ふというで】 (n) big arm

so maybe this submission would not be  out of place in  the main dictionary.