The Vancouver protocol and its definition of authorship has been mentioned in many questions of this kind here on Academia but I think they deserve being repeated. The protocol describes authorship through three components which every author must fulfil:

1. Conception and design, or analysis and interpretation of data

AND

2. Drafting the article or revising it critically for important intellectual content

AND

3. Final approval of the version to be published.

A key point here is the "AND". To read and comment on the text is clearly not enough for authorship by these standards. In fact a reviewer of the manuscript would at least fulfil point 2 whereas a person helping out as you describe would not.

It is difficult to fend off this behaviour from more senior colleagues as a PhD student. It may, however, be good to bring up an open discussion about authorship standards in the group without necessarily directly connecting it to the draft of a paper. In some research groups systems for determining both order and authorship as such have been developed by splitting the paper up into tasks. See for example, AuthorOrder.com for an example. Looking at the authorship tag here on Ac.sx and a search on Google will provide much background. But, I particularly recommend the recommendations report from [ICMJE (International Committee of Medical Journal Editors)].(http://www.icmje.org/recommendations/)

The so called Vancouver protocol (developed by ICMJE (International Committee of Medical Journal Editors) and its definition of authorship has been mentioned in many questions of this kind here on Academia but I think they deserve being repeated. The protocol describes authorship through three components which every author must fulfil:

1. Conception and design, or analysis and interpretation of data

AND

2. Drafting the article or revising it critically for important intellectual content

AND

3. Final approval of the version to be published.

A key point here is the "AND". To read and comment on the text is clearly not enough for authorship by these standards. In fact a reviewer of the manuscript would at least fulfil point 2 whereas a person helping out as you describe would not.

It is difficult to fend off this behaviour from more senior colleagues as a PhD student. It may, however, be good to bring up an open discussion about authorship standards in the group without necessarily directly connecting it to the draft of a paper. In some research groups systems for determining both order and authorship as such have been developed by splitting the paper up into tasks. See for example, AuthorOrder.com for an example. Looking at the authorship tag here on Ac.sx and a search on Google will provide much background. But, I particularly recommend the recommendations report from ICMJE; ICMJE developed the protocol and their recommendations constitutes their continually updated version of the protocol.