Summary and descriptive text in any section should be composed of proper sentences and NOT just phrases.
1. Start with a capital letter
2. End with period, question mark or exclamation
3. Should not be written in all capital letters
4. Should be complete and meaningful
5. Should be simple, should tell one thing per sentence
6. Should not be too long with too many words. (Any sentence with more than 15 words will be very hard to understand)
Look at the following sample text.The following are NOT sentences, but they are phrases:
|Nokia is a good phone manufacturer. Lasts long. Priced reasonably well. Release new phones every year. Easy to use. Does not break easily.|
The above is an invalid paragraph since it uses phrases instead valid sentences.
To make it a valid paragraph, it can be modified like this:
|Nokia is a good phone manufacturer. The phones made by Nokia last longer than other phones. Their phones are priced reasonably well. Also, Nokia releases new phones every year. Their phones are easy to use and do not break easily.|
The above text shows how the phrases are converted to valid sentences. If you are interested in learning the grammar involved in constructing a proper sentence, read more here: http://www.learnenglish.de/grammar/sentencetext.htm
When phrases are allowed?
Phrases are allowed in few scenarios "list of items". For an example, look at the text shown in the list (number 1 to 5) in brown color above. All the 5 points mentioned are phrases and not sentences, which are allowed in a list.
In most cases, we prefer paragraphs made by sentences and not list. If it is unavoidable, you may use lists with phrases.