The 1950s and 60s saw a shift in understanding and attitudes towards mental illness.
Generally, mental illness was not well understood. Those who suffered from mental health issues, such as Phil's mum, were often isolated in asylums and stigmatised in their communities.
The establishment of the NHS in 1948, the development of tranquilising drugs and a growing awareness that patients were entitled to human rights all contributed to a change in how people with mental health issues were viewed and treated.
The value and ethics of treatments such as electro-convulsive therapy (a process involving inducing seizures with electricity) and institutionalisation were increasingly questioned.
The 1959 Mental Health Act abolished the distinction between psychiatric and other hospitals and encouraged the development of community care.
Phil clearly has fears about his mother's health, and possibly his own. He deals with the subject secretly (discussing it only with his most trusted friend, Spanky). This highlights the shame associated with mental illness and the challenges of dealing with it openly during this era.