http://www.newsbtc.com/2015/11/15/bitcoin-and-the-deflationary-spiral-a-double-edged-sword/
This question had been discussed a lot a couple of years ago. The main argument in the piece by the link seems to be that Bitcoin is an infinitely divisible currency and the amount of coins needed for transactions will reduce proportionally as its price rises. But that is irrelevant to the cause which brings about deflationary spiral. In other words, if the reason given were true, then deflationary spiral wouldn't be possible since you can always add zeroes to a currency unit via denomination reforms (in this case subtract zeroes). Obviously, it won't and couldn't work in practice because deflation is not caused by the lack of decimal places and you can't fix it by adding more, which is what the claim made basically comes down to.