Probably this article will give you some answer.

I am sorry that this is out of my exerpertise. We can learrn from the previous report in the following.

Int J Pharm. 2000 Mar 10;196(2):215-8.

Degradation of phosphatidylcholine in liposomes containing carboplatin in dependence on composition and storage conditions.

Pietzyk B1, Henschke K.

Abstract

In this study, the hydrolytic degradation of phosphatidylcholine in aqueous liposome-dispersions and the stability of the anti cancer drug carboplatin enclosed in the liposomes were investigated in dependence on liposome composition and storage conditions. Cholesterol containing liposomes show a high stability of the phosphatidylcholine and the encapsulated carboplatin during six months storage in refrigerator. The hydrolytic degradation of phosphatidylcholine is strongly increased by addition of the antioxidant ascorbyl palmitate, but despite the partial hydrolysis the advantages of the lipid membrane are retained-- no degradation of the drug and no changes in the particle size were detected during six months storage in refrigerator, in contrast to storage at room temperature.

PMID:10699721  [PubMed - indexed for MEDLINE]  (from PubMed)

To answer your question, let us understand what kind of molecule phosphatidylcholine, otherwise known as lecithin is.  It is a phosphoplipid and together with amphipathic lipids form the membrane 'skeleton'. 

Phophatidylcholine consists of phosphate, 2 fatty acids, glycerol and an alcohol which in this case is choline.  Lecithin is also part of an enzyme lecithin cholesterol acyl transferase.  Now to answer your question, the make up of lecithin does not tolerate high temperature.  100oC  is the boiling point of water and that is more than enough to boil  and break the alcoholic (ester) link, or denature any enzyme or protein.  Besides, you are considering the component of living cells, at a temperature as high as 100 o C neither the cell or its components can have any cellular integrity.  Components of cell membranes or cell membranes  are usually stored in freezers at  minus 10oC  (at the least degrees) and below for structural and functional stability.  You are dealing with an organic molecule.  What you would have at that high temperature cannot be lecithin. 

Thank you for your answer. However, The related article claims that certain period of time (60 min) would not change the phospholipid composition lecithin up to 150 degrees celsius.

My goal is to solubilize lecithin into oil to achieve homogenious solution. Can this be done at 70 degrees celsius without significant degradation of phosphaytidyl choline?

I am sorry, I have not seen the related article you are referring to but I believe you have the address of the author of that article or he probably is following your request and may be able to answer your question.  All my work on plamsa membrane were strictly under very cold conditions.  If I can understand you, it appears you will like to isolate it rom the membrane and that of course calls for the disruption of the membrane itself.  What we used for membrane work was red blood cells for obvious reasons and a combination of buffers of different ionic strength and centrifugation (refrigerated MSE centrifuge) with different conditions for different component and of course at different speed and time. 

You can find the article in the beginnig of the conversation. Thank you very much for your answers!

 Interesting reference from Cassio. 

Since PC shows a high proportion of PUFA, you should also consider non-hydrolytic changes, as those related to the oxidative degradation of fatty acids, that might change the fatty acid profile of the PC upon heating. 

Yes, Jorge.... Your observation is great!