Should I get a PhD?
The length of typical PhD programs varies a lot; my disciplines however there are generally 2-3 years of coursework, followed by 1-3 years of dissertation. In some fields (e.g., history), this timeline is definitely longer but it is rarely shorter than 4-5 years. PhD programs provide a lot of autonomy so how long someone takes to complete it will depend on many factors.
Do they have financial support and/or funding? Many programs offer assistantships which provide tuition remission, health insurance (and other benefits), and a stipend. Or do they have to work full or part-time while in school? Some programs accommodate working students better than others.
How involved is your mentor? Are they difficult to meet with? If you go into a PhD program with a very clear goal and research agenda having a mentor who is less involved may not matter. But, if you're like many students and need more guidance in course selection, defining research goals, career guidance, a less available mentor will definitely make your program longer.
Do you have or will you have children during this time? Most PhD programs do not provide maternity leave for graduate students so if you need to take time off for your children that will make your program longer AND you could risk losing your funding if you are funded through an assistantship.
And most importantly, what are you professional goals? I typically only recommend that people pursue a PhD for one of two reasons: 1) you want a career in research and/or academia, or 2) you work in a field where you can only be promoted with an advanced degree and you already have a Masters. PhD programs are long and (can be) expensive. And while they do carry a lot of clout, the actual skills that you can transfer to non-academic or research careers are somewhat limited. Getting a PhD because it sounds interesting or would be nice is probably not worth the time, money, effort, and mental and emotional exertion.
When choosing a PhD program you should look at how long other students took to finish (keeping in mind faster isn't necessarily better), as well as what sort of jobs they got after graduation. Are those the types of jobs you would want?
Pros & Cons
Pros: The intellectual process of a PhD can be incredibly rewarding if you love and are passion about what you are studying. You also earn tremendous credibility by completing something that so few actually complete.
Cons: It is DIFFICULT! If it were easy everyone would do it. Not only can be the content be extremely challenging and the workload large, but you need to be incredibly self-regulated to complete a PhD program. So much of the work does not have deadlines or anyone over-seeing you so it is on you to make sure your work gets done, that you seek out the support and resources that you need, learn the things you need to learn, and ultimately reach the goals you want to reach. The great thing is that in many fields (e.g. educational psychology) there are wonderful support networks within programs and within professional organizations. But you do need to take the initiative to seek them out.