I saw this in an official communication from the number-two executive at the world’s largest telecommunications company.

Problem:
An apostrophe is missing.

Explanation:
The singular noun “world” requires a possessive apostrophe followed by an “s” to indicate the possession of the “best communications company” by the world. Another way to write this phrase is “Building the best communications company in the world …”.

Solution:
“Building the world’s best communications company …”